1. Field of the Invention
The present invention regards a system for reducing signal disturbances in electrocardiogram (ECG), which disturbances are caused by cardio-pulmonary resuscitation.
2. Description of Related Art
The three primary means of treating sudden cardiac death are cardio-pulmonary resuscitation (CPR), defibrillator shocks and medication, cf. the publications [1] xe2x80x9cAdvisory Statements of the International Liaison committee on Resuscitation (ILCOR). Circulation 1997;95:2172-2184, and [2]xe2x80x9dGuidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Carexe2x80x9d. Journal of the American Medical Association, Oct. 28, 1992, Vol. 268 No 16: 2171-2302.
The normal course of action in the case of sudden cardiac death and a resuscitation attempt is to first administer CPR until the defibrillator arrives, and then alternate between shocks from the defibrillator and CPR until the patient has a distinct pulse or until an ALS team arrives (ALS=Advanced Life Support). Then, securing of the respiratory passages and use of medication will be included together with the alternating use of a defibrillator and CPR. The first step towards resuscitation is to restore spontaneous heart activity and sufficient blood pressure. This is often termed ROSC (Return of Spontaneous Circulation).
The protocol that guides the defibrillator-CPR treatment states that, upon arrival of the defibrillator, three shocks should be administered initially, followed by 1 minute of CPR, then three new shocks and so on [1]. In order to administer a shock, the ECG must first be measured, analysed and classified as xe2x80x9cTreatxe2x80x9d or xe2x80x9cNotreatxe2x80x9d. Defibrillators of the automatic or semi-automatic type will do this automatically, and this type of defibrillator is often called an AED (Automated External Defibrillator). The part of the software that performs this classification is usually described as the VF algorithm. After concluding the rhythm, the defibrillator will ready itself for shock delivery, report its readiness to deliver shocks, and wait for the user to operate the shock button. This procedure takes time, and it takes about one minute to administer three shocks. This is time during which the patient does not receive CPR, and during which vital organs, especially the brain, is damaged further due to the lack of blood supply [1].
Furthermore, this procedure entails the shock being delivered approximately 20 seconds after the CPR has been concluded. Animal experiments have shown that the probability of achieving ROSC decreases rapidly with time from conclusion of the CPR. The best chance of achieving ROSC is through delivering the shock without delay following CPR, cf. the publication [3] by Sato Y, Weil M H, Sun S et al., titled xe2x80x9cAdverse effects of interrupting precordial compressions during cardiopulmonary resuscitationxe2x80x9d in Crit Care Med 1997;25:733-736.
Performance of CPR has a disturbing effect on the ECG signals. The disturbances take the form of rhythmic signals, and occur simultaneously with heart compressions or inflations. As heart compressions are administered at a rate of 80-100 per minute, these rhythmic disturbances will generally cause the VF algorithm to draw incorrect conclusions in those cases where the rhythm is VF (ventricle fibrillation) or VT (ventricle tachyardia). This is caused by the algorithm interpreting the rhythmic disturbances as a pumping rhythm; i.e. there is no requirement for defibrillator shocks. It is therefore normal procedure to use the VF algorithm only after CPR has been concluded, cf. publication [1].
The present invention regards a system that reduces the disturbances in the ECG during heart compression though use of adaptive digital filtering as stated in the introduction. The following advantages are derived from the invention.
As the VF algorithm can conclude while CPR is being performed, this will lead to less time being used for shock delivery, thereby leaving more time for CPR.
For the same reason, the shock may be delivered sooner following the conclusion of the CPR, something that will directly increase the probability of ROSC.
It becomes possible to perform signal analysis of VF for other purposes than classification. A useful possibility is to measure the characteristics of the heart that may indicate how effective the CPR is.